Apparatus for the stabilization of ships



Oct. 15, 1957 J. BELL APPARATUS FOR THE STABILIZATION OF SHIPS 2Sheets-Sheet 1 Filed March '7, 1952 %/A/vPL/F/El? 2 771 15 GYQOSCOPE f/Aw/va H25 SP/NDLE AX/S MOUNTED ATHWAQTISH/P Z 7 vaoc/ry SEA/SA alum/13651,

Oct. 15, 1957 J. BELL APPARATUS FOR THE STABILIZATION OF SHIPS FiledMarch 7, 1952 2 Sheets-Sheet 2 lVlET/JDYNE Unite APPARATUS FOR THESTABILIZATION OF SHIPS John Bell, Beckenham, England, assigior toMnirhead & Company Limited, Beckenham, England This invention relates tothe stabilization of ships, which may be carried out in known ways as,for example, by means of movable fins or hydroplanes, water jets or thelike. The invention is adapted for use with any of these means but isparticularly suited to the control of movable fins or hydroplanes and isdescribed in relation thereto.

The fins are structures which project from the sides of the ship,usually on the curve of the hull between the upright portion and thebottom, and are mounted upon shafts so that they may be tilted in orderto impose a torque upon the ship to counter the roll.

The natural rolling motion of a ship is harmonic in character but thismotion is, in the practical case, dis turbed by Wave motion, wind andother factors. Nevertheless the roll tends to have a periodic timeapproximating to the natural periodic time of the ship, so that largeand small roll cycles tend to occupy the same time period but the rollvelocity varies. In known ship stabilisation arrangements two gyroscopesare employed, one being a vertical keeping or pendulous gyro and theother a velocity sensitive gyro. Signals derived from these gyros areapplied in any desired combination to control gear which, in turn,governs the movement of the heavy torque-producing means.

The sensing means must be of high sensitivity in order to provideeffective stabilisation against small degrees of roll and they must alsoprovide correct signals under conditions of heavy rolling without manualadjustment, to ensure that the stabiliser is fully automatic. It is alsoimportant that the changeover time of the stabilising means from port tostarboard torque or vice versa be kept short since two changes arerequired in each roll cycle; desirably the two changes should not occupymuch more than 20% of the roll cycle time. The size of the stabilisingmeans is subject to certain practical limitations includingconsiderations for the stability of the ship and, in general, is notadequate to supply a torque sufficient to counter the heaviest degree ofroll. Under such conditions the stabilising means can effect a largereduction in the roll amplitude but cannot provide full stabilisation.

Sensing apparatus of high sensitivity and quick response is incapable ofproducing large mechanical forces to initiate control signals and if thecontrol gear imposes an appreciable load or reaction back, the sensingmeans may be prevented from following the ships movement freely and thecontrol signal will therefore contain errors. To avoid this difiiculty,elaborate systems have been devised in which the control gear isincapable of reacting back on the sensing means.

An object of the invention is to provide a simplified control system forthe stabilisation of ships employing a velocity sensitive gyroscope only(omitting the vertical keeping gyro) arranged so that the fin deflectionfrom the zero torque position is related to roll velocity up to themaximum deflection or torque of the stabilising means and for all rollvelocities above this maximum the sta- States Patent ice bilising meansremain in the maximum position, but reaction back on the gyro whilst thestabilising means are in the maximum position does not cause an error insubsequent movements of the gyro.

According to the invention, a control arrangement for the stabilisationof ships comprises one gyroscope only, of the velocity-sensitive type,together with means by which the torque-producing means are controlledin a proportional or graduated manner up to a maximum torque value overa relay mechanism having a limited travel and allowing reaction back onthe gyro when the said relay mechanism reaches the limit of its travel.Such reaction back affects the movement of the gyroscope whilst thestabilising means are in the maximum position but causes no error in itssubsequent movements within the proportional range.

The relay may consist of an electronic, magnetic or hydraulic amplifierand may include synchro or magslip systems and hydraulic servo motors.

The invention will be further described with reference to theaccompanying drawings in which:

Figure l is a diagrammatic layout of one arrangement in accordance withthe invention.

Figure 2 shows a modification of Figure 1.

Figure 3 is a further arrangement.

Figure 3a is an end view of a part of Figure 3.

Figure 4 shows a modified form of Figure 3.

Figure 5 shows a modified form of Figure 1.

In a practical construction according to the invention a velocitysensitive gyroscope 1 is employed, mounted in known manner with itsspindle athwartships, so that the wheel spins in a vertical planeparallel to the fore and aft axis of the vessel. The gyro is mountedaccording to the known art in such a manner that it has one degree offreedom only, that is to say, the gyro in its casing may be rotatedabout an axis 20 substantially normal to the deck plane of the ship. Anarm 21 is attached to the casings of gyro 1 and is linked to thejunction of two springs 22 and 22' and the remote ends of the springsare anchored to a part of the fixed structure. The springs urge the gyrointo its normal position in which its axis is athwartships. When theship rolls, the spin axis of the gyro is forced to tilt with it and thegyro tends to turn about the axis in which it is free, i. e. it developsa precessional torque which is proportional to the velocity with whichthe spin axis is moved out of its original plane. This torque is opposedby the centralising springs so that the actual movement of the gyroagainst the springs is proportional to velocity. This is a Well-knownarrangement and is referred to as a velocity sensitive gyroscope.

The gyroscpoe may be coupled to control gear directly by mechanicallinkage or may conveniently be coupled by the use of synchronoustransmission units known as synchros or magslips, which are similar incharacter. Thus the movement of gyro 1 causes a corresponding rotationof the rotor of transmit synchro or magslip 2 through the medium of thegear and lever system shown.

synchro is a generic term covering data transmission units, includingmagslips, and these are of a form akin to small electric motorscomprising a stator having three equally spaced windings similar tothose of a three-phase induction motor and a rotor which may have one ormore windings. If the stator windings of two such units are connectedtogether line-to-line and single rotor windings in the two units areconnected to an A. C. supply, then the alternating field due to eachrotor will, by transformer action, induce voltages in its respectivestator windings having magnitudes depending upon their positions withrespect to the axis of the rotor winding. If the two rotors are indifferent angular positions, the respective stator voltages will notbalance and out-of-balance currents flow between the two stators. Thesecur- 3 rents set up additional fields which cause equal torque to beexerted on the two rotors to move them into coincident positions, inwhich the stator voltages balance and no torque is exerted on eitherrotor. If one rotor is used as a master and is moved, then the secondrotor will act as a slave and will follow.

The movement of the rotor of transmit synchro 2 is reproduced by therotor of receive synchro 3. The rotor of synchro 3 operates a sensitivehydraulic valve 4 which in turn controls the movement of a pair ofhydraulic pistons 5 and 5 actuating an appropriate lever system 6. Thestructure of valve 4 is old and well known in the art of hydraulic powersystems. The force available at synchro 3, which is of the order of afew grams, is thus increased in value to a force which may lie between10 and 160 pounds and the stroke is likewise increased to a travel ofthe order of one-inch. This larger control force is used to operate apowerful hydraulic system which directs the torque-producing means.

In operation, gyro 1 precesses in one direction or the other accordingto the direction of the ships movement and to an extent depending uponthe roll velocity. Its movement is transmitted mechanically to transmitsynchro 2 and thence over the transmission lines to receiver synchro 3The movement of this arm operates sensitive hydraulic valve 4.

The length of the valve 4 will be such that when the proportional rangeof operation is exceeded, there will be a reaction back on the gyro,which, however, as previously mentioned, will introduce no error in thecontrol system.

In a practical case it may, for example, be found desirable that themaximum stabilising torque shall be applied when the angular rollvelocity reaches 2 per secnd, and the fins are then tilted to theirmaximum angles. For roll velocities lower than 2 per second, the finangles are proportionately smaller but when the roll velocity exceeds 2per second by any amount, the fins remain tilted to their maximumangles. Operation of the control under conditions of heavy rolling isthus discontinuous to the extent that during that part of each roll inwhich the roll velocity exceeds 2 per second, the torque-producing meansremain in full operation in the desired sense, but when the rollvelocity falls below this predetermined figure, the torque-producingmeans are controlled in a proportional or graduated manner.

When the roll velocity reaches the predetermined maximum, the movementof the arm coupled to the spindle of transmit synchro 2 is such that arm23 of synchro 3 comes into contact with stops 9. Any movement of arm 24beyond the position at which arm 23 is held by the stops encountersextra resistance due to the nature of the synchro transmission system.This increased resistance is communicated to gyro 1 and is added to theresistance offered by springs 22 and 22 and the movement of gyro 1 isrestricted just as would be the case if stronger springs were used.This, however, causes no error in later movements of the gyro since itremains in the precessed position until the roll velocity drops belowthe maximum when it begins to move back to its central position and arm23 moves away from the stop. When arm 23 reaches one of the stops 9, themovement of valve 4 is stopped and the torque-producing means are alsostopped in the corresponding position.

Piston 5 operates lever system 6 through a lever 25. A pivoted lever 26,in conjunction with a link 27, forms a parallel lever system. The lowerpiston 5 bears against lever 26, and, in this way, the separationbetween the pistons is constant but the pistons are, nevertheless, freeto move in unison.

A further pivoted lever 23 which pivots about a pin 29 is carried in ablock attached to the ships structure. Lever 28 is linked to the body ofsensitive valve 4 by a link 30 engaging lever 28 at an intermediatepoint 31.

When synchro arm 23 moves in either direction from its central position,valve 4 is opened in one direction or the other. This allows hydraulicliquid to flow into one or the other of the closed chambers belowpistons 5 and 5. The piston which is energized begins to move andactuates the lever 6. It also causes lever 28 to move the body of valve4 in such a direction as to close the valve. This will be recognized asa normal servo follow-up which ensures that the controlled mechanismfollows the movement of the controlling mechanism exactly.

Alternatively, other forms of electro-mechanical relay may be used tooperate the hydraulic control.

Thus, Figure 2 shows the transmit synchro supplying a rectifier circuit7 (connections are taken from two of the three stator phases), toprovide a circuit for operating an electro-magnetic relay 8 which inturn operates the sensitive hydraulic valve 4.

A further alternative shown in Figures 3 and 3a would be to use atransmitter 2 of the synchro type, again as the control link, but inthis case supplying a coincidence transmitter or synchro controltransformer 10 giving an ele trical output instead of a mechanicaloutput which would be used as a receiving instrument feeding to a relayor other force-producing means 12. Thus the signal to the controltransformer 10 will endeavour to cause the shaft connecting the controltransformer to the fin 16 to turn. In so far as it is unable to do so, asignal will be transmitted to relay 12. The relay or otherforce-producing means is followed up by a hydraulic system;alternatively, as shown, the output may be applied to an electricalgenerator system such as a metadyne (a dynamo-electric amplifier) 12(Fig. 3), or alternatively, an amplidyne or a Ward-Leonard system; sucha system operating a powerful motor 13 whose duty it is to operate thetorque-producing means for stabilisation of the ship. In such a systemthe torque reaction on the transmitter is generally not large but againby the method of control used, namely, a velocity sensitive gyro, noerror in the control is introduced.

A further feature, however, which is desirable for electrical control isto restrain or suitably control the torque of the main power motor whenthe fin or other torqueproducing means has been moved to the end of itstravel. With the electrical link urging further movement of the motor, amaximum torque effort would be produced and, further, the inertia of themotor is required to be arrested at the end of the travel in order toavoid over-stressing of the motor, the gears and the other parts of themechanism. A method of achieving this is, as shown, to introduceelectrical control elements 14' which may be-of a potentiometer type or,alternatively, inductive type such as synchro, etc. located at thetorque-producing means in such a way that they come into operation onlyas the limits of movement are approached.

Thus the motor 13 drives a wheel 15 operating the fin 16 and a radiusarm 17 on the wheel 15 towards its desired limits of travel engages oneor other of the radius arms 18 respectively on the shafts of the controlelements 14. In the last few degrees of movement the rotation of thecontrol elements produces a progressively increasing voltage which maybe fed back to the amplifier 11 or to the metadyne system 12 in such away as to oppose the signal from the magslip or synchro controltransformer 10. Such a synchro control transformer is one whose primaryis supplied with electrical angular information from the transmitsynchro 2 and whose secondary transmits or supplies electricalinformation or furnishes output impulses dependent upon the impulsesignals or information received from the transmit synchro and theposition of the fin means 16. In this way a balance will be achieved inwhich the torque output generated by the motor will be just sufficientto keep the fin or other torque-producing means in the desired positionsubstantially at the limit of movement.

The limiting device may be applied in duplicate, as shown, oralternatively one limit device with appropriate mechanical connectinglevers may be employed to provide limits for each direction of motion.

In a further arrangement of remote control, linear inductive devices,transducers, or potentiometers may be used instead of magslips orsynchros, the system operating on a balance of voltage between thepotentiometer or other device controlled by the gyro and thecorresponding instruments coupled to the fin or torque-producing means.

Following known technique, a resetting transmitter of whatever type maybe mechanically coupmd to the motor with precise gearing, the purpose ofthis re-arrangement being to avoid hunting due to possible back-lash inthe main drive to the torque-producing means.

The operation by the velocity sensitive gyro of a suitable relay by amechanical linkage is shown in Figure 5 which is the same as Figure 1but with the synchro transmission system taken out.

Various other modifications may be made within the scope of theinvention.

I claim:

1. A control apparatus for a stabilizing system for vessels and whichsystem is of the type in which movable fin means projecting from thehull of the vessel constitute torque producing means for stabilizingpurposes, said control apparatus including in combination with a vesselincluding a hull, a movable fin means, a single gyroscope comprising avelocity sensitive gyroscope mounted with its spindle axis athwartshipso as to spin in a vertical plane parallel with the fore and aft axis ofthe vessel, said gyroscope having only one degree of freedom about avertical axis and being rotatable about an axis substantially normal tothe deck plane of the vessel whereby the angular velocity of rolling ofthe vessel will cause a precessional torque to be exerted by thegyroscope deflecting from zero up to a predetermined maximum that isproportional to the velocity with which the spindle axis is moved,spring means operatively associated with the gyroscope to oppose thetorque and urge the gyroscope into normal position with its axisathwartship whereby the torque is converted into movement that isproportional to the rolling velocity, a transmit synchro, coupling meansbetween said gyroscope and said transmit synchro so that the latterfurnishes impulse signals responsive to gyroscope deflection, a synchrocontrol transformer means connected to said fin means, means couplingsaid transmit synchro to said synchro control transformer means so thatthe latter is responsive to said gyroscope deflection and furnishesoutput impulses dependent upon the impulse signals received from thetransmit synchro and the position of the fin means, power impartingmeans for actuating the fin means, coupling means between the synchrocontrol transformer means and the power imparting means and actuated bythe impulses from the synchro control transformer means to actuate thepower imparting means to correspondingly actuate the fin means betweenzero deflection position and predetermined maximum positions in oppositestabilizing movements and means limiting the travel of the fin means inopposite stabilizing movements at least as the fin means approach amaximum position in said movement so as to allow reaction back on saidgyroscope at least when said fin means are in a maximum position torestrict further movement of said gyroscope until roll velocity fallsbelow maximum.

2. A control apparatus as claimed in claim 1 in which the powerimparting means comprises an electric motor and the coupling meansbetween said synchro control transformer means and said motor comprisesan electrical generating system operable in response to output signalimpulses from said synchro control transformer means to correspondinglyactuate said motor.

3. A control apparatus as claimed in claim 2 and the means limiting theextent of travel of the fin means including electrical control meansactuated in response to the fin means approaching the limit of traveland operably associated with the electrical generating system betweenthe synchro control transformer means and the motor to furnish impulsesto said system operative to reduce the torque output of the motor so asto keep the fin means in a position substantially at the limit of traveluntil the rolling velocity falls below maximum.

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